Optical properties and I–V characteristics of ZnO nanostructures grown by electrochemical deposition on Si (1 1 1) and Si (1 0 0)

• Different morphology of ZnO electrochemically deposited on Si (1 1 1) and Si (1 0 0) substrates.
• Ohmic behavior of Al–ZnO–Al MSM UV-detector.
• A considerable enhancement in UV detector performance.
• ZnO nanoflake show high sensitivity at room temperature to UV illumination.
• The ZnO nanoflakes showed higher photoresponsivity than ZnO pyramids.

ZnO nanostructures were grown using the electrochemical deposition method from Zn (NO3)2⋅6H2O on Si substrate with different crystallographic orientations. Scanning electron microscopy results showed the ZnO nanostructures developed two different shapes, nanoflakes along Si (1 1 1) and pyramids-like shape on Si (1 0 0). X-ray diffraction results revealed that the deposited ZnO was crystalline with a hexagonal wurtzite phase. Room temperature photoluminescence spectrum showed a stronger ultraviolet peak for the nanoflakes that were grown on Si (1 1 1) than pyramids-shape like grown on Si (1 0 0) with the same green emission (deep-level emission (DLE)) intensities. Therefore, it can be concluded that Si substrate orientation played the most important role in shaping the structural and optical properties of ZnO nanostructure. The crystallinity of materials and the defects in the crystal structure were studied through Raman spectroscopy. Aluminum formed an ohmic contact on MSM UV PD indicated by linear relationship between current and bias voltage. Our results showed that photoresponse properties of the photodetectors strongly dependent on the surface to volume ratio. The nanoflakes ZnO enhanced UV detection performance, high sensitivity and shortened rise times compared to pyramids-shape like ZnO. We showed that photodetectors based on nanoflakes (high surface to volume ratio) ZnO have a faster response than ones based on pyramids-shape like ZnO.